The present invention relates to a model for measuring a stress distribution as a simulation model of a cast or forged product, and a method of measuring a stress distribution of a cast or forged product by using such a simulation model.
The stress distribution analysis of machine parts is usually carried out by computer simulation or by measuring stress distributions of actual parts. However, when the cast or forged metal products have complicated shapes, stress distributions are usually measured by first preparing samples of the same materials and applying a load thereto to measure their strains.
For the strain measurement of such cast or forged products, various methods are utilized, and particularly a strain gauge method is widely used for the reasons that it is relatively simple and suitable for quantitative measurement.
In this strain gauge method, a plurality of resistance wire strain gauges are attached onto a cast or forged product itself, and a load of the same intensity as an actual load is applied onto the cast or forged product to measure its stress distribution. Based on the stress distribution measurement results, various measures such as reinforcement of portions having insufficient strength, reduction of thickness of portions showing excessive rigidity, etc. are conducted. By repeating the stress distribution measurement, further working is conducted to achieve the desired shape of the cast or forged product showing satisfactory stress distribution.
Accordingly, until the optimum shape showing a uniform stress distribution is obtained, actual cast or forged products should be made several times, and stress distribution measurement should be repeated on each cast or forged product, taking a lot of time and labor. Particularly in the case of developing new parts, the period necessary for such development is inevitably long.
In view of this circumstance, it has been tried to produce models made of softer materials than actual cast or forged products and analyze their stress distributions from their load-strain relations, and as materials for such models, glass, epoxy resins, etc. have been proposed. In the case of stress distribution analysis by using models of such materials, a photoelasticity test method is sometimes used. However, it requires a highly trained operator and an expensive apparatus.
The inventors previously proposed the measurement of strain on an integral model constituted by a polyurethane foam which is attached with a plurality of resistance wire strain gauges at its predetermined sites and subjected to a load (Jidosha Gijutsukai Ronbunshu (The Journal of Automobile Technology Society), No. 27, 1983, pp. 84-90; Castings, Vol. 57, No. 8, pp. 485-490 (1985)). By a method using this polyurethane foam model, it is possible to know the general tendencies of stress distributions in actual cast or forged products. However, because of support sheets of resistance wire strain gauges and adhesives for bonding the gauges to models, large measurement errors are inevitable, and high skill is required for this measurement. Thus, it was proposed, as described in the article in "The Journal of Automobile Technology Society," to provide undercoating layers under adhesives for attaching the gauges. However, the application of undercoating layers alone was unable to solve the problems of measurement errors.
In addition, since the polyurethane foam has an extremely different face-friction coefficient from those of metals such as steel, etc. and has an extremely larger ratio of Young's modulus to specific gravity than those of metals, large measurement errors are generated depending upon supporting methods of polyurethane foam models.